812 THE ORIOLW OF SPECIES 



and longest lamina in tlie Greenland whale is ten, twelve, 

 or even fifteen feet in length; but in the different species 

 of Cetaceans there are gradations in length; the middle 

 lamina being in one species, according to Scoresby, four 

 feet, in another three, in another eighteen inches, and in 

 the Balsenoptera rostrata only about nine inches in length. 

 The quality of the whalebone also differs in the different 

 species. 



With^ respect to the baleen, Mr. Mivart remarks that 

 if it "had once attained such a size and development as 

 to be at all useful, then its preservation and augmentation 

 within serviceable limits would be promoted by natural 

 selection alone. But how to obtain the beginning of such 

 useful development?" In answer, it may be asked, why 

 should not the early progenitors of the whales with baleen 

 have possessed a mouth constructed something like ths 

 lamellated beak of a duck? Ducks, like whales, subsist 

 by sifting the mud and water; and the family has some- 

 times been called Criblatores^ or sifters. I hope that I 

 may not be misconstrued into saying that the progenitors 

 of whales did actually possess mouths lamellated like the 

 beak of a duck. I wish only to show that this is not 

 incredible, and that the immense plates of baleen in the 

 Greenland whale might have been developed from such 

 lamellae by finely graduated steps, each of service to its 

 possessor. 



The beak of a shoveller-duck (Spatula clypeata) is a 

 more beautiful and complex structure than the mouth 

 of a whale. The upper mandible is furnished on each f 

 side (in the specimen examined by me) with a row or 

 comb formed of 188 thin, elastic lamellae, obliquely 

 bevelled so as to be pointed, and placed transversely 



